A resin molded article is used as a substitute for a metal from the standpoint of weight reduction of various components, but there is often the case where it is difficult to substitute all the metal components with a resin. In this case, it may be considered that a metal molded article and a resin molded article are bonded and united to produce a novel composite component.
However, a technique capable of bonding and uniting a metal molded article and a resin molded article by an industrially advantageous method with a high bonding strength has not yet been subjected to practical use.
JP-B 4,020,957 describes an invention of a laser processing method of a metal surface for bonding with another material (resin) comprising a step of laser scanning the metal surface in one scanning direction, and a step of laser scanning in a scanning direction crossing the same.
JP-A 2010-167475 describes an invention of a laser processing method of the invention of JP-B 4,020,957, in which the laser scanning is performed plural times in a superimposed manner.
However, in the inventions of JP-B 4,020,957 and JP-A 2010-167475, the laser scanning is necessarily performed in two directions crossing each other, and thus there is room for improvement in such a point that the processing time required is too long.
Furthermore, it is considered that the laser scanning in the crossing directions may sufficiently roughen the surface to enhance the bonding strength, but there is a problem that the surface roughness state may not be uniform, and thus the directionality of the strength of the bonding portion of the metal and resin may be unstable.
For example, there may be a problem that one of the bonded articles has the highest shearing force or tensile strength in the X-axis direction, but another one of the bonded articles has the highest shearing force or tensile strength in the Y-axis direction, which is different from the X-axis direction, and still another one of the bonded articles has the highest shearing force or tensile strength in the Z-axis direction, which is different from the X-axis and Y-axis directions.
There is a case where such a resin-metal composite article that has a high bonding strength in a particular direction is demanded depending on the product (for example, a rotating member in one direction and a reciprocating member in one direction), but the inventions of JP-B 4,020,957 and JP-A 2010-167475 may not sufficiently meet the demand.
In the case where the bonding surface has a complicated shape or a shape containing a narrow portion (for example, a star shape, a triangular shape and a dumbbell shape), such a case may be considered that the laser scanning method in the crossing directions partially roughens the surface to make the surface-roughening treatment non-uniform, and as a result a sufficient bonding strength is not obtained.
JP-A 10-294024 describes a production method of an electric or electronic component by forming an unevenness on a metal surface by irradiation with a laser light, and a resin, rubber or the like is injection-molded on the portion having the unevenness formed thereon.
The embodiments 1 to 3 describe the formation of the unevenness on a surface of a metal long coil by laser irradiation. The paragraph No. 10 describes that the surface of the metal long coil is surface-roughened in a stripe form or a satin finish, and the paragraph No. 19 describes that the surface of the metal long coil is surface-roughened in a stripe form, a broken line form, a wavy line form, a knurl form or a satin finish.
However, as described in the effect of the invention in the paragraphs Nos. 21 and 22, the purpose of the laser irradiation is to form fine and irregular unevenness on a metal surface, thereby enhancing the anchoring effect. In particular, the target to be treated is a metal long coil, and therefore it is considered that fine and irregular unevenness is necessarily formed in all the cases of forming any type of unevenness.
Accordingly, the invention of JP-A 10-294024 describes the same technical concept as the invention of forming a fine unevenness on a surface by laser irradiation in the crossing directions as in the inventions of JP-B 4,020,957 and JP-A 2010-167475.
WO-A 2012/090671 relates to an invention of a production method of a composite molded article formed of a metal molded article and a resin molded article. The invention has a step of forming marks containing straight lines and/or curved lines on a bonding surface of a metal molded article in the same direction or different directions by laser scanning, in which the laser scanning is performed in such a manner that the marks each formed of straight lines and/or curved lines do not cross each other. FIGS. 6 to 9 show the marking patterns in a quadrangular shape, a circular shape, an elliptical shape and a triangular shape.